It has been common practice for many years to provide two separate valves in a fluid-carrying pipe when it is desired to prevent back flow of the fluid. One type of shut-off valve, known as a ball valve, has been provided to shut off the flow of fluid when desired and a check valve has been additionally provided downstream from the ball valve to prevent back flow of the fluid in the event of a loss of pressure downstream from the ball valve.
The expense and inconvenience of installing two separate valves can be avoided according to the disclosure in U.S. Pat. No. 4,846,221 for BALL VALVE WITH BUILT-IN CHECK VALVE, issued Jul. 11, 1989 to Kitz Corporation of Tokyo, Japan upon application of Tonaharu Kanemaru. The Kanemaru patent discloses a valve casing having a ball with a built-in check valve that is moved into operable position when the ball is rotated to the open position in the usual fashion to permit the flow of fluid. This built-in check valve is an improvement over the prior practice of using two separate valves.
But, check valves inevitably need repair or replacement. When Kanemaru's check valve needs either repair or replacement, it is first necessary to close a shut-off valve upstream from the damaged check valve, then remove the valve casing containing the damaged check valve, and then remove the ball from the valve casing to gain access to Kanemaru's check valve within the ball. The parts of Kanemaru's check valve 3 requiring repair or replacement must then be dis-assembled and replaced with operative parts which need be carefully re-assembled within Kanemaru's ball 2 in order for his movable valve body 7 to operably register with the valve seat 6 in Kanemaru's ball 2.
The aforesaid difficulty and inconvevience of gaining access to a valve within a ball is obviated by the disclosure in U.S. Pat. No. 3,146,792, issued Sep. 1, 1964, to Donnelly. Donnelly shows a ball 3 with an excess flow valve assembly 31 inserted in the hole in the ball, and a lateral extension 11 for gaining access to the excess flow valve assembly 31 when the ball 3 is turned to the closed or shut-off position. The outer end of Donnelly's chamber 13 is closed by a threaded cap 63, which may be removed with a conventional tool for access to the excess flow valve assembly 31.
Neither Kanemaru or Donnelly show a modular check valve in the ball. Donnelly's easily removable threaded cap 63 is dangerous because of the possibility of the cap 63 being accidentally or maliciously removed while the ball 3 is turned to the open or on-line position; or maliciously removed for the purpose of tampering with the valve or contaminating the contents of the pipe line system in which the valves are installed.